The present invention relates to an improved process for preparing alkyl-transition metal complexes in particular monoalkylmetallocenes and dialkylmetallocenes, and to a process for preparing solutions of such compounds which are directly suitable for use in the polymerization of olefins.
Monoalkylmetallocene and particularly dialkylmetallocene compounds can in combination with specific cocatalysts, such as, for example, aluminoxanes or, in particular, triphenylboron derivatives, tetraphenylborate derivatives and alkylaluminum fluorides, form highly active catalyst systems (J. Organomet. Chem. 1992, 434.C1-C5, Organometallics 1991, 10, 3910; J. Am. Chem. Soc. 1989, 111, 2728; EP-A-O 522 581; EP-A-0 468 537).
Processes hitherto known in the literature for preparing monoalkylmetallocene and dialkylmetallocene compounds (in particular dimethyl compounds) in which lithium alkyls or alkyl Grignard compounds are used, have a series of disadvantages.
As a result of the use of methyl Grignard or methyllithium, the syntheses are tied to polar solvents such as, typically, diethyl ether or tetrahydrofuran. However, these solvents are catalyst poisons for the application in olefin polymerization, so that after the reaction of the metallocenes with the corresponding alkylating agent, the solvent has to be completely removed and the compound has to be isolated in pure form.
Furthermore, depending on the metallocene, the yields in their reactions to give the corresponding alkyl derivatives are very variable. (Chemistry of Organo-Zirconium and -Hafnium Compounds", D. J. Cardin, M. F. Lappert, C. L. Raston, 1986, Ellis Horwood Limited, 145-180; "Organometallic Chemistry of Titanium, Zirconium and Hafnium", P. C. Wailes, R. S. P. Coutts and H. Wiegold, 1974, Academic Press, Inc., 92-97, 150-151, 185-187; Gmelins Handbook of Inorganic Chemistry, Volume 10, Organo-Zirconium Compounds, 1973, Verlag Chemie--Weinheim/Bergstrasse, p. 54-58; Gmelins Handbook of Inorganic Chemistry, Volume 11, Organo-Hafnium Compounds, 1973, Verlag Chemie--Weinheim/Bergstrasse, p. 12).
It is therefore an object of the present invention to develop a process which overcomes these disadvantages of the prior art and by means of which the pure alkyl-transition metal compounds either can be prepared directly in high yields or even can be obtained without additional work-up steps directly in the solutions of the alkyl-transition metal compounds which are free of catalyst poisons and can be used in olefin polymerization.